The present invention relates to instructive displays, and more particularly to displays for optical instruments which provide symbolic instruction to assist an operator in centering an optical element on a path.
Many optical instruments, and particularly ophthalmic instruments, require an operator to center an optical element on a path, such as a light path. Lens testing instruments and ophthalmic instruments, such as lensmeters, tonometers, refractors and the like, all require the centering of an optical element on a path. Lensmeters are used to inspect and measure the power of lenses and require centering the lens on a light path, while tonometers and refractors require that the eye be centered with respect to a path. A number of prior art devices utilize a CRT display and require an operator to superimpose two dots and center them with respect to a circle drawn or projected on a screen. U.S. Pat. Nos. 4,511,227, issued Apr. 16, 1985, and 4,705,045, issued Nov. 10, 1987, disclose a tonometer using this type of centering device. Such devices rely heavily on operator skill and intelligence to translate the location and spacing of the two dots into a direction and the amount of motion required to center the object. This heavy reliance on skill and intelligence severely limits the practitioner's choice of operators for performing routine tasks. Other devices have used a CPU to determine the location of the center of a light pattern on a detector and provide an operator with a display of the X-Y location of the component relative to a center path.